1. Field of Invention
This invention pertains to micro-adaptive thresholding of a color image.
2. Description of Related Art
U.S. Pat. No. 4,442,544 to Moreland et al., incorporated herein by reference in its entirety, discloses a micro-adaptive thresholder for processing image pixels. As discussed in the '544 patent, a portion or block of one or more image pixel lines is examined. The maximum and minimum pixel density of the examined portion or block is determined. The difference between the maximum and minimum pixel density in the portion or block is then determined. That difference is multiplied by a predetermined constant, which represents a desired change in threshold level, to provide a base threshold. The base threshold is differenced from the maximum pixel density to provide an optimum threshold.
U.S. Pat. No. 5,778,092 to MacLeod, et al., incorporated herein by reference in its entirety, discloses a technique for compressing a color or gray scale pixel map representing a document. The '092 patent uses a thresholding technique by generating a bitmap of binary values. The thresholding process is adaptive and is based on the pixel values in a local neighborhood around a target pixel. The process, shown in FIGS. 6A and 6B of the '092 patent, involves generating a sum of all pixels which differ in density by a certain maximum value. An average value of all the pixel intensities (or densities) that contributed to the maximum difference is then found. This average value of maximum pixel intensity (or density) difference is used as the threshold.